Binding of a protein (repressor) to the operator sequence in an operon thus preventing the transcription of the following structural gene(s) into mRNA and consequently synthesis of protein (cf. enzyme repression).
Source:
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 164 (https://doi.org/10.1351/pac199264010143)